The present invention relates to a wireless communications device that has a common RF interface that receives WCDMA (Wideband Code Division Multiple Access) signals and LTE (Long Term Evolution) signals, and a baseband circuit that separates and combines WDCMA and LTE signals.
In recent years, use of 3GPP LTE as a high volume and high speed communications system has begun. A LTE system may select an arbitrary channel bandwidth from a frequency bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz. There may be cases where the LTE may be a Third Generation (3G) communications systems using adjacent frequency bands and WCDMA. Focusing on cases where WCDMA and LTE use adjacent frequency bands, the development of wireless communication systems (hereinafter referred to as “dual mode device”) supporting the functionality of both WCDMA and LTE modes has been advancing. The dual mode device with an RF antenna can simultaneously communicate using both WCDMA and LTE signals that are on adjacent carrier frequencies, for example, a WCDMA system may be used for voice communications while an LTE system may be used for communicating high volumes of non-voice data.
FIG. 1 schematically illustrates a prior art wireless communication device 10 (dual mode device) that may operate using WCDMA and LTE. As shown in FIG. 1, the wireless communication device 10 includes an antenna 12, a duplexer 14, an RF receiving portion 16, an RF transmission portion 18, and a baseband circuit 20. The RF receiving portion 16 includes a two system receiving RF interface that includes a first receiver RF interface 30 (hereinafter referred to as “first RRF-IF”) for LTE use and a second receiver RF interface 32 (hereinafter referred to as “second RRF-IF”) for WCDMA use, so that both LTE and WCDMA signals may be separately processed.
In regards to the first RRF-IF 30, a BPF 34 extracts an LTE signal 36 from a band limited signal 28. A quadrature modulator (QDEM) 38 that functions as center frequency (IF) circuit uses a differential frequency (fLu−fu) of the LO frequency fU and the carrier center frequency fLU of LTE, to demodulate the LTE signal 36, and generate analog IQ data 40. An ADC 42 generates digital IQ data 44 by A/D converting analog IQ data 40 at a given sampling frequency based on the received channel bandwidth. The digital IQ data 40 is supplied to an LTE receiving portion 46 of the baseband circuit 20. The LTE receiving portion 46 includes a discrete Fourier transformer 48 (DFT) connected to the ADC 42. The DFT 48 converts the digital IQ data 44 from the ADC42, namely the resulting baseband signal as the information symbol of the time domain, to a subcarrier signal 50 shown as an information symbol (frequency spectrum) of the frequency domain according to the DFT size corresponding to the received channel bandwidth.
The second RRF-IF 32 has a BPF 52 that extracts a WCDMA signal 54 from the band limited signal 28. A QDEM 58 functions at center frequency (IF), using the differential frequency (fWu−fU) of LO frequency fU and the carrier center frequency fWu of WCDMA, to demodulate the WCDMA signal 54, and generate analog IQ data 58. An ADC 60 generates digital IQ data 62 by A/D converting the analog IQ data 58 at the given oversampling frequency based on the WCDMA chip rate (3.84 Mcps). The digital IQ data 62 is processed by a WCDMA receiving portion 64 of the baseband circuit 20.
The RF transmission portion 18 similarly includes a two system RF transmission interface for separately processing the LTE and WCDMA signals, namely, a first transmission RF interface 70 (hereinafter “first TRF-IF”) and a second transmission RF interface (hereinafter “second TRF-IF”) that are respectively connected to an LTE transmission portion 66 and WCDMA transmission portion 68 of the baseband circuit 20. The LTE transmission portion 66 includes a discrete inverse Fourier transformer 74 (IDFT). The IDFT 74 converts a subcarrier signal 76 of information symbols in the frequency domain to digital IQ data 78 shown as a time domain information symbol according to the IDFT size corresponding to the transmission channel bandwidth.
The first TRF-IF 70 has a DAC 80 that D/A converts the digital IQ data 78 from IDFT 74 to an analog signal and provides the analog signal quadrature demodulator (QM) 82 using the differential frequency (fLd−fd) of LO frequency fd and the carrier center frequency fLd of LTE to generate an LTE signal. Afterward, the frequency band of the LTE signal is limited to the given transmission channel bandwidth by BPF 84.
The second TRF-IF 72 has a DAC 88 that D/A converts digital IQ data 86 from the WCDMA transmission portion 68 and a QM 90 uses the differential frequency (fWd−fd) to generate the WCDMA signal. The WCDMA signal band limited by BPF 92. An up converter 94 uses the LO frequency fd and converts each of the WCDMA and LTE signals from the first and second TRF-IF 70 and 72 to the transmission frequency. The unnecessary frequency components are removed by BPF 96 and the transmission power is amplified by power amplifier (PA) 98 so that the RF transmission portion 18 transmits the LTE and WCDMA signals.
The structure shown in FIG. 1 shows a double conversion method that uses the differential frequency to generate IQ data 40 and 58 (zero IF signal) after primarily converting the received frequency to the IF signal corresponding to the LO frequency fu. However the down converter 24 may be omitted if only a single conversion is required, and the LO frequency fu is set to zero. Similarly, the RF transmission portion 18 may omit the up converter 94.
Referring to FIG. 2, the processes of the first RRF-IF 30 and second RRF-IF 32 of the RF receiving portion 16 will be explained in detail. For ease of comprehension, FIG. 2 shows the case where the RF receiving portion 16 performs single conversion (i.e., fu=0).
For example, when wireless communication device 10 continuously receives 5 MHz bandwidth WCDMA signals and 15 MHz bandwidth LTE signals, BPF 34 of the first RRF-IF 30 and BPF 52 of the second RRF-IF 32 operate independently to extract LTE signal 36 and WCDMA signal 54, respectively. In the LTE path, the LTE signal 36 is demodulated by QDEM 38 then A/D converted by ADC 42. The sampling frequency of the ADC 42 is fixed at the integrated value of the DFT size (1536 corresponding to 15 MHZ in FIG. 2) corresponding to the received channel bandwidth and subcarrier interval (fixed value of 15 kHz). Digital IQ data 44 is generated by the ADC 42 and supplied to the DFT 48. At the same time, the LTE receiving process is operating in parallel. WCDMA signal 54 is demodulated by QDEM 56 then A/D converted by ADC 60 in the WCDMA path. For WCDMA, the ADC 60 uses an oversampling frequency that is several times (4×, 8×) the chip rate (3.84 Mcps) to improve sensitivity. FIG. 2 shows an oversampling frequency of 4 times the chip rate set at 15.36 MHz. As such, digital IQ data 62 is generated by ADC 60 and supplied to the baseband circuit 20.
Thus, the communication device 10 includes both RRF-IF 30 and 32 at RF receiving portion 16, with respective ADCs 42 and 60, QDEMs 38 and 56, and BPFs 34 and 52. Similarly, the transmitter portion 18 includes both TRF-IFRF 70 and 72, and respective DACs 80 and 88, QMs 82 and 90, and BPFs 92 and 96. For this reason, a circuit-scale sized RF interface is relatively large and consumes a lot of power.
FIG. 3 shows another prior art wireless communication device 100. The wireless communication device 100 includes transmitter and receiver portions of the RF interface for a WCDMA/LTE wireless device. As compared to the wireless device 10 of FIG. 1, the wireless device 100 has an ADC 102 and a DAC 104 for the WCDMA and LTE links. Also, a Quadrature Modulator (QM) 106, down converters 108, 110, and filters 112, 114 in the RF receiver path perform the digital processing with up converters 116, 118 and filters 120, 122 in the RF transmission path. The dotted line portion in FIG. 3 shows the digital circuit portion.
When receiving, the down converter 24 converts an RF signal to an IF signal at the first LO frequency f1u. QM106 has as an input the second LO frequency f2u (<f1u) and generates digital IQ data from the output of ADC 102. In the LTE path, down converter 108 generates baseband signal 124 as a zero IF signal based on the differential frequency (fLu−fu; where fu=f1u+f2u) of the carrier center frequency, fLu, and LO frequencies, f1u and f2u. The baseband signal 124 is supplied to multiplexer 126 via filter 112. Meanwhile in the WCDMA path, down converter 110 generates baseband signal 128 as the zero IF signal based on the differential frequency (fLu−fu) of the carrier center frequency, fWu, and WCDMA LO frequencies, f1u and f2u. The baseband signal 128 is supplied to multiplexer 126 via filter 114, which is a RRC (Root-raised Cosine) filter.
The multiplexer 124 time division multiplexes the WCDMA baseband signal 128 and the LTE baseband signal 124 and generates CPRI signal 130. The CPRI signal 130 is provided to demultiplexer 132, which separates the received CPRI signal 130 into WCDMA and LTE baseband signals and supplies the LTE baseband to LTE reception unit 46 (DFT 48), and supplies the WCDMA baseband to WCDMA reception unit 64. The transmission processing is basically the same as the receiving process explained above except in reverse. More specifically, CPRI signal 136 is time division transmitted from multiplexer 134, and separated into LTE baseband signal 140 and WCDMA baseband signal 142 at demultiplexer 138. In the LTE path, the LTE baseband signal 140 is digitally processed at rectangular filter 120 and up converter 116, while in the WCDMA path, the WCDMA signal 142 is digitally processed at RRC filter 122 and up converter 118. The outputs of the LTE and WCDMA paths are provided to DAC 104 and the output of the DAC 104 is provided to Quadrature Modulator (QM) 144, which modulates the analog signal output by the DAC 104. Up converter 94 modulates the individual frequencies of the LTE and WCDMA signals to the transmission frequency and then LTE and WCDMA signals are filtered by BPF 96, boosted by PA 98, and then transmitted with the antenna 12.
In FIG. 3, fd has the following relationship fd=f1d+f2d, where f1d>f2d. Thus, FIG. 3 shows that in the wireless communication device 100, the ADC102 and DAC104 are shared by WCDMA and LTE signals. However as with the wireless communication device 10, the digital IQ data is processed in parallel in two independent paths. In the transmission and receiving paths in the structure of FIG. 3, WCDMA and LTE paths use the rectangular filter 120 and RRC filter 122, respectively. The Quadrature Demodulator 106 is shared by WCDMA and LTE, and then is connected to down converter 108 for LTE processing and down converter 110 for WCDMA processing. Similarly, the Quadrature Modulator 144 is shared by WCDMA and LTE, but then is connected to up converter 116 in the LTE path and up converter 118 in the WCDMA path. As a result, as the filter and frequency modulator use two independent RF interfaces, a relatively large amount of power is still consumed. Having two separate paths also increases circuit area. Thus, there is a need for a device that consumes less power and requires less circuit space.